First-line chemotherapy with doxorubicin (Dox) is the current standard of care for patients with advanced, symptomatic soft tissue sarcoma (STS), but dosage is limited by cardiotoxicity. This is particularly problematic in STS because there is evidence that tumor response rates correlate with dosage. Further, local control and/or limb salvage can be achieved using regional therapy (isolated limb infusion techniques, regional chemotherapy with radiation or preoperative systemic chemotherapy with local hyperthermia). These findings support the need for a local non-invasive Dox delivery platform with low systemic toxicity for treatment of STS. To address this unmet need, this proposal seeks to improve Dox delivery to STS and reduce cardiotoxicity by developing an image-guided targeted drug delivery platform utilizing liposomes, ultrasound contrast agents or microbubbles (MBs), and externally applied ultrasound (US). We have recently developed a Dox-loaded delivery vehicle comprising liposomes containing Dox conjugated to polymer MBs, or Dox-loaded lipopolyplexes (DoxLPX), which can be i.v. injected. When circulating shell- encapsulated MBs are exposed to appropriately tuned US, they expand and contract, inducing micro-scale fluid dynamic phenomena and bio-effects --increased vascular and cellular permeability through sonoporation and induction of endocytosis-- that facilitate liposomal drug unloading, cellular drug delivery and uptake. Notably, navigation of the US beam confers both imaging of the treatment area as well as spatial targeting of the therapeutic effect, excluding non-target regions from drug release. We have demonstrated that specific US pulses release 70% of the loaded Dox from DoxLPX, preferentially delivers Dox to murine squamous cell carcinomas (SCC) in vivo with less cardiac accumulation compared to Dox alone, and inhibits SCC tumor growth, raising exciting possibilities for enhanced tumor-specific drug delivery and release. We will test the overall hypothesis that i.v. injected MBs carrying Dox, combined with tumor directed US, improves local Dox accumulation, inhibits tumor growth and reduces drug-induced cardiomyopathy in a murine STS solid tumor model (orthotopic fibrosarcoma). Our Specific Aims are: Aim 1: To determine the pharmacokinetics and biodistribution of Dox resulting from US delivery of DoxLPX. Aim 2: To determine the anti-tumor efficacy and cardiotoxicity of US-mediated DoxLPX delivery. Aim 3: To investigate the DoxLPX release mechanisms using ultra-high speed microscopy Ultimately, this proposal will establish the foundations for a powerful theranostic platform for delivery of Do that combines the advantages of liposome encapsulation with a novel US-MB delivery strategy to augment liposomal Dox release specifically at the tumor site, while reducing off-target effects. Since liposomal Dox and MBs are mature technologies with precedent for FDA approval, we view strong potential of combining them for localized Dox delivery with fast-track to clinical translation, ultimately improving prognosis in patients with STS.